1. Technical Field of the Invention
The invention relates generally to communication systems; and, more particularly, it relates to synchronization of communication between various devices within such communication systems.
2. Description of Related Art
Data communication systems have been under continual development for many years. In recent years, WPANs (Wireless Personal Area Networks) have been under increasing development. A WPAN may be viewed as a network that is established when two or more devices connect to support communication of data between themselves in an area having a radius of up to approximately 10 meters. Typically, earlier implementations of WPANs include a central PNC (piconet coordinator) that governs the communication of all of the other communication devices within the WPAN. Also, any of the communication devices within such a WPAN is typically capable of operating as the PNC.
As is known, the Bluetooth® communication standard is the first such PAN (Personal Area Network) communication standard that has been developed. In accordance with the Bluetooth® communication standard, the communication between the various devices in such a WPAN is strictly performed using an M/S (Master/Slave) configuration. Each of the devices within such a Bluetooth® WPAN is M/S capable. Typically one of the devices (sometimes referred to as piconet controller in this situation), or a first device within the Bluetooth® WPAN, transmits a beacon signal (or an access invitation signal) while operating as the “master” device of the Bluetooth® WPAN to the other “slave” devices of the Bluetooth® WPAN. In other words, the “master” device of the Bluetooth® WPAN polls the other “slave” devices to get them to respond.
However, other WPANs may be implemented such that the devices do not operate according to such an M/S (Master/Slave) type relationship. Typically, some of the communication devices within the WPAN are designated and operate as PNCs, and some of the communication devices are designated and operate as DEVs (wireless communication devices within the WPAN are not PNCs). The PNCs operate to coordinate the communication between themselves and the DEVs within the WPAN. Sometimes, such a PNC may be implemented to operate as a master with respect to the 1 or more DEVs that operate as slaves, but this need not be the case in all instances—the strict M/S relationship is typically the case only in a Bluetooth® WPAN.
In even some other instances, two or more Bluetooth® piconets operate cooperatively such that they communicate via the masters of the two or more corresponding Bluetooth® piconets. For example, in a scatternet, a single DEV may interact with two or more masters. This implementation will allow various devices within different piconets that are located relatively far from one another to communicate with one another via the masters of their corresponding piconets. However, within a scatternet implementation, a problem may arise such that each of the individual piconets must be able to operate in relative close proximity with other piconets without interfering with one another. This inherently requires a great deal of synchronization between the piconets, which may be very difficult to achieve in some instances. It is also noted that independently operating piconets, not implemented within a scatternet implementation, may also suffer from deleterious effects of interference with other piconets located within relative close proximity.
Some PAN communication standards and recommended practices have been developed (and some are still being developed) by the IEEE (Institute of Electrical & Electronics Engineers) 802.15 working group. These standards and recommended practices may generally be referred to as being provided under the umbrella of the IEEE 802.15 working group. Perhaps the most common standard is the IEEE 802.15.1 standard which adopts the core of Bluetooth® and which generally can support operational rates up to approximately 1 Mbps (Mega-bits per second).
The IEEE 802.15.2 recommended practice specification has been developed primarily in an effort to support the co-existence of the IEEE 802.15.1 Bluetooth® core with IEEE 802.11b and IEEE 802.11g WLANs (Wireless Local Area Networks). As some examples of the pertinent frequency spectra of concern, the IEEE 802.11b and IEEE 802.11g WLAN (Wireless Local Area Network) standards both operate within the approximate 2.4 GHz frequency range. The IEEE 802.11a WLAN standard operates within the approximate 5 GHz frequency range. This IEEE 802.15.2 recommended practice specification has been developed to ensure that such a WLAN and a Bluetooth® piconet may operate simultaneously within relatively close proximity of one another without significant interference with one another.
In addition, the IEEE 802.15.3 high data rate PAN standard has been developed in an effort to support operational rate up to approximately 55 Mbps. In this IEEE 802.15.3 standard, the PNCs and DEVs do not operate according to an M/S relationship as they do according to Bluetooth®. In contradistinction, a PNC operates generally as an AP (Access Point) and manages the various DEVs such that they are guaranteed to perform their respective communication according to their appropriate time slots thereby ensuring proper performance and operation within the piconet. An extension (currently under progress) of the IEEE 802.15.3 high data rate PAN standard is the IEEE 802.15.3 WPAN (Wireless Personal Area Network) High Rate Alternative PHY Task Group 3a (TG3a). This is sometimes referred to the IEEE 802.15.3a extended high data rate PAN standard, and it can support operational rates up to 480 Mbps.
Yet another standard developed by the IEEE 802.15 working group is the IEEE 802.15.4 low data rate PAN standard that generally supports data rates within the range of approximately 10 kbps (kilo-bits per second) and 250 kbps.
One of the major concerns when operating a WPAN (that may include multiple SOPs relatively close to one another) is the undesirable interference that can occur between the devices of different piconets. There are at present, insufficient means by which this undesirable interference may be minimized.